COS 123-10
A test for ecotypic differentiation in the competitive ability of beneficiary species found under nurse-plants and in open sites in arid systems
The positive effect of nurse-plants on beneficiary species can act as a selection process affecting competitive ability of these recipient species. The purpose of this study was to determine if there is evidence for changes in competitive ability of species that associate with nurse-plants but maintain a presence in open sites in arid ecosystems. Seeds from species found growing under shrubs and in the open in a South American Desert ecosystem were collected and grown in sets of growth chambers programmed to emulate the microenvironmental conditions of each. Each source was reciprocally planted and simple density series were used to contrast performance in germination and early seedling establishment lifestages to infer changes in competitive ability.
Results/Conclusions
This design is an excellent extension to the reciprocal common garden design now used to study invasive plant species from different regions and the analog of differentiation within species but at much smaller scales is an important topic to consider for the study of plant faciitation and positive interactions more generally. Importantly, density-dependent interactions between beneficiary species is an important concept in modeling community dynamics and changes in apparent competition could be an important factor that mediates the capacity for shrubs to buffer the loss of smaller plant species within arid systems. Specifically, there was a strong signal of ecotypic differentiation detected in this study with individuals from the understorey source possessing increased competitive abilities. Importantly, this also supports the emerging hypothesis that indirect interactions, primarily negative, are often greater in the context of overarching facilitation by dominants.